The invention relates to an apparatus for making a drilled hole with an undercut.
A drilling apparatus is known for making a drilled hole with an undercut, in particular in facing panels of stone, ceramics, concrete or similar material, comprising a drive device providing means for rotating a hollow drilling shaft; a drill bit holder held in the hollow drilling shaft so as to be rotatable with the hollow drilling shaft; and a drill bit having a drilling head provided with laterally projecting cutting edges and held in the drill bit holder to project from the drill bit holder.
To produce drilled holes with an undercut, drilling devices are known in which the entire drilling tool is swivelled to ream out the undercut. By swivelling out the drilling tool while simultaneously performing a stirring movement, the lateral cutting edges arranged on the drilling tool ream out an undercut in the region of the bottom of the drilled hole. An expansible fixing plug with an expansible sleeve can be inserted and fit into the hole with the undercut.
Such drilled holes with an undercut can also be made in facing panels or similar structures, but those undercuts must be made very exactly, so that, when an expansible fixing plug is inserted and expanded, the expansion pressure that is produced is not too great. Too great an expansion pressure can result in a part of the facing panel breaking away. In order to produce an exact undercut, these drilling tools are designed so that they produce an automatic, machine-controlled swivelling-out action. In addition, drilling tools that have a drilling head set with diamond chips are used. As the drilling tool clamped in alignment with the drive axis of the drilling machine penetrates into the facing panel, the entire end face of the truncated conical drilling head engages with the facing panel.
DE-A1 41 19 350 discloses a device for producing drilled holes with an undercut in facing panels, in which the drilling machine and also the drill bit attached thereto are pivoted from the center line and are positively guided along a cam plate during the reaming-out operation to produce the undercut.
EP-A2 0 336 182 discloses a drilling apparatus for providing a drilled hole with an undercut in which the drill bit is pivotally secured to the drilling shaft. The drill bit used in that specification has a widened drill head which is able to ream out an undercut in a drilled hole when the drill bit is positioned obliquely.